Method of making electrical contact discs



May 3, 1966 J. R. LUSH METHOD OF MAKING ELECTRICAL CONTACT DISCS Original Filed May 8, 1961 United States Patent 3,248,780 METHOD OF MAKING ELECTRICAL CONTACT DISCS John R. Lush, Zion, Ill., assignor to Fansteel Metallurgical Corporation, a corporation of New York Original application May 8, 1961, Ser. No. 108,518, now Patent No. 3,192,351, dated June 29, 1965. Divided and this application Aug. 10, 1962, Ser. No. 216,081 6 Claims. (Cl. 29155.55)

This invention relates to the method of making electrical contacts from rods of tungsten and other refractory metals.

This application is a division of my copending application Serial No. 108,518, filed May 8, 1961, now Patent No. 3,192,351, entitled Electrical Contact Discs and Method of Making Same.

Electrical contacts are often made out of materials such as tungsten or ceramics by complicated forging and grinding operations. These relatively expensive procedures are necessary to obtain a generally spherical contacting surface which is desired to provide a low resistance junction between the contact points. This configuration insures smoother circuit breaking by reducing arcing.

In accordance with the present invention, there is provided a method whereby electrical contact discs having the desired surface properties can be manufactured at a relatively low cost. This is accomplished by introducing a rod of electrical contact material into an area where it is engaged by a cutting device such as a rotating wheel or oscillating saw blade that enters the rod at an angle of less than 90 relative to the rod axis and is moved in its own plane.

In order to cut a contact disc having a conical surface, the cutting device is maintained at a fixed angle after it enters the rod. If a disc having a spherical surface is desired, the angle of the cutting device is continuously varied between the angle at which it enters the rod and 90.

The conical discs then may be introduced into a tumbling device or other similar apparatus to form the cone face into a surface having a substantially spherical radius.

The novel articles which can be produced by this method include an electrical contact which may be conical at both ends or one which has a contacting surface at one or both ends that is generally conical in shape but which has a round apex, rectilinear medial portion, and a rounded junction between the conical face and disc body portion.

Apparatus that is capable of performing these methods are described in the following specification and illustrated in the accompanying drawings in which:

FIGURE 1 is a plan view of an apparatus which can be used for producing contact discs;

FIGURE 2 is a series of enlarged and exaggerated views showing the cutting action which takes place in forming a contact disc having a conical contact surface when the axis of the wheel and the axis of the rod are in the same plane;

FIGURE 3 is a section taken along lines 33 of FIGURE 2;

FIGURE 4 illustrates a finished generally conical contact disc;

FIGURE 5 is a view showing the cutting action which takes place in forming a contact disc having a spherical contact surface;

FIGURES 6a and 6b are two views showing the cutting action that takes place in forming a contact disc having conical surfaces at both ends; and

FIGURE 7 shows a finished disc having a conical front and back surface.

The apparatus shown in FIGURE 1 is illustrated in schematic form and is but intended to be exemplary of apparatus that could be used to cut conical and spherical discs from a rod of electrical contact material. As disclosed therein, there is shown mounted on a machine base 1, a rod supporting, rotating and feeding assembly including a rod spindle housing 2 through which rod 3 extends. The rod 3 is held in place in the spindle housing by a collet 4. The rod 3 and collet 4 are rotated by a rod spindle drive motor 6 through pulley 7, belt 8, and pulley 9. An air motor (not shown) or other equivalent device may be used to move rod 3 axially into a cutting area where it is cut into discs. 'In the disclosed machine, the rod 3 is biased against a rod stop 12 mounted in a bracket 13.

In the illustrated embodiment, the rod 3 is cut into discs by a cut-off wheel 14. The wheel 14 is a thin fiber or steel disc which cuts the rod into discs by moving in the direction of the plane of the disc. The axes of the wheel and rod are in the same plane. The wheel 14 is power-driven by a motorized spindle 17 supported by spindle housing 18. The housing 18 is slidably mounted on a table 16 through a tongue 22 that moves in groove 23 cut into a plate 24 secured to table .16.

The table 16 is pivotally mounted relative to the base 1 at pivot 15, the axis of which intersects the axis of rod 3 at right angles. As will be seen hereinafter, this relationship is essential when cutting discs having a spherical surface. The table 16 may be rotated about pivot 15 by a hydraulic motor 26 that is secured to base 1. The motor 26 may be continuously operated to swing table 16 about pivot 15 or may be utilized to adjust table 16 to a fixed angle relative to base 1. The operation of motor 26 will depend on whether it is desired to cut discs having conical surfaces or those having spherical surfaces. The operation of the various components described above will be discussed in detail when considering the various methods covered by this application.

While it is not disclosed in the schematic view shown in FIG. 1, it is within the scope of this invention to provide a means for displacing the axis of the cutting wheel in a plane normal to the plane containing the axes of rod 3 and wheel 14 when they are in the position shown in FIG. 1.

When it is desired to out conical discs, the cut-off wheel 14 is disposed at an angle of less than relative to the axis of rod 3 by hydraulic motor 26. The hydraulic motor is then locked in place to retain table 16 in a fixed position. As shown in FIG. 2, the cut-off wheel 14 cuts aconical surface on the front end of one disc and a slightly concave surface on the back end of the disc being cut off. The concavity results from the angular relationship between the cut-oft wheel and rod 3 and the diameter of rod 3 (see FIG. 3.)

If it is desired to cut discs 30 having conical contacting surfaces 30a, 3012, at both ends, as shown in FIG. 7, the axis of the cut-off wheel is displaced one-half the diameter of the cut-off wheel in a plane perpendicular to the direc tion of movement of the cut-off wheel during cutting. Allowance should be made, of course, for necessary clearances. The relationship between the cutting wheel and rod when cutting such double-conical discs is shown in FIGS. 6a and 6b. Briefly, due to the displacement of the wheel and rod axes, the portion of the wheel to the right of the center, as shown in FIG. 6b, is cutting a conical surface on the back face of the disc before the disc is severed from the rod. A disc having a part conical and part concave back surface can be obtained by displacing the axis of the cut-off wheel less than one-half the diameter of the wheel.

The apparatus disclosed herein can also be utilized to cut discs having a spherical radius from an elongated rod of contact material. This is accomplished by introducing the cut-off wheel to the rod at an angle of less than 90 and continuously varying the angular relationship between the rod and the cut-off wheel until it reaches 90. The varying relationships between the cutting wheel 14 and rod 3 are shown in FIG. 5. This is accomplished by operating motor 26 to oscillate table 16 about pivot 15. During this operation, the axes of wheel and rod 3 are located in the same plane. The location of pivot 15 in the same plane and normal to the axis of rod 3 insures that wheel 14 will be disposed normal to the axis of rod 3 during the final cut which severs a spherical disc from the rod.

While it is not illustrated, the subject apparatus could be provided with a brake or other mechanism for preventing axial movement of the rod while the cutting wheel is being withdrawn from the rod. This serves to minimize the wear imposed on the cutting wheel 14 and thus lengthen its useful life.

The cutting action that takes place when cutting conical or spherical disc-s with a cutting device, such as a wheel or a cutter having a straight edge, is as follows:

During the cutting of conical surfaces, the cutting device is moved in the plane of the cutter at an acute angle to the axis of the rod to cut the rod along substantially onehalf a chordal length at the depth of cut. In the case of a cutting wheel, the cutting takes place along an are between a point on the wheel which is on a line connecting the axes of the rod and wheel at the depth of cut, and a point at the intersection of the rod with the wheel. The curvature of the are cut by the wheel is determined by the relationship between the diameter of the wheel and the diameter of the rod (see FIGURE 3.). As the wheel increases in diameter, the cut more closely approaches one-half a chord. When a straight-edge cutting device such as a saw or wire is used, a full one-half chord will be cut by the cutting device at the depth of cut. The one-half chord that is being cut extends along a line between a point on the straight-edge cutting device :at the depth of cut that is on a line normal to the cutting edge and extends through the axis of the rod, and a point at the intersection of the rod and cutting device. It is obvious that only half a chord is cut since cutting only takes place during the infeed of the cutting device and on the infeed side of the rod as it rotates with respect to the cutting edge of the cutting device.

The cutting action above described also applies to cutting spherical surfaces, since a spherical surface is essentially made up of a number of cuts, each of which, except the last, are made in a plane disposed at an acute angle to the axis of the rod. The plane in which the cut takes place varies with each cut to form the essentially spherical surface. The last cut, which severs the disc from the rod, is made in a plane normal to the axis of the rod.

In summation, it can be seen that when cutting either conical or spherical surface, the cutting device enters the rod in a plane disposed at an acute angle to the rod and throughout all of its cutting travel is cutting along substantially one-half a chord of the rod at the depth of cut.

If the use to which the conical discs are put requires that the surface of discs 25 or 30 be rounded off, the contacts are placed into a tumbling device. The amount of tumbling to which the contact disc is subjected determines the final configuration of the surface of the disc. The discs are generally tumbled until the contacting surface is one that is generally conical in shape, but which has a rounded apex 28a, an intermediate rectangular portion 28b, and a rounded juncture 280 between the generally conical face and the disc body portion 29 (see FIG. 4). However, if desired, the discs could be formed until the contact surface has a substantially spherical radius. The discs so formed are readily usable where a low resistance junction between contact points is required.

The details of the mechanisms which can be employed to accomplish the foregoing operations are not important to an understanding of the present invention. However, it is noted that specific apparatus which can be used to accomplish the methods to which this application is directed is disclosed in two patent applications S.N. 108,447, now Patent No. 3,186,133 and SN. 108,448, now Patent No. 3,174,257 which were filed in the name of William M. Maki and assigned to the assignee of the present invention.

With the disclosed or similar apparatus, contact discs can be produced with contacting surfaces that can be used in electrical apparatus without requiring further machining. This can be done with relatively simple machine tools at a high rate of speed with the result that contact discs can be produced at a relatively low cost compared with those presentlyv being manufactured by forging or grinding.

As previously mentioned, the apparatus illustrated is intended to be merely representative of various machines that could be used to cut discs having conical or spherical surfaces. It is obvious that, if desired, the power-driven cut-off wheel could be fixed in place and the rod moved into engagement therewith instead of as illustrated in the drawing. Also, the wheel could be stationary and only the rod rotated. Furthermore, the driving means for the rotating disc and the arrangement of the power-driven spindle are merely exemplary since other arrangements could be employed. Other equivalents will occur to those skilled in the art and it is, of course, intended to cover by the appended claims all such embodiments as fall within the true spirit and scope of the invention.

I claim:

1. The method of producing electrical contact discs from an elongated rod of contact material comprising rotating the rod, bringing the rotating rod and a planar wheel cutting device into cutting relationship with the rod and relatively moving the cutting device and the rod in a plane at an acute angle to the axis of the rod to sever the rod by progressively cutting the rod along substantially one-half a chordal length at the depth of cut.

2. The method as disclosed in claim 1 in which the cutting device is maintained in the plane disposed at an acute angle to the axis of the rod to cut a disc having a conical contacting surface.

3. The method as disclosed in claim 1 in which the acute angle between the cutting device and the axis of the rod is continuously varied toward to cut a disc having a substantially spherical face.

4. The method of producing electrical contact discs having a conical surface from an elongated rod of contact material comprising rotating the rod, bringing the rotating rod and a cutting wheel into cutting relationship, relatively moving the rod and the cutting wheel into cutting engagement at an angle between the rod and the cutting wheel of less than 90, and cutting discs from said rod while maintaining the said angular relationship.

5. The method of producing electrical contact discs having a conical surface from an elongated rod of contact material comprising rotating the rod, longitudinally moving the rod into engagement with a .rod limiting means, moving a cutting wheel in its own plane into cutting relationship with the rod at an angle between the rod and and wheel of less than 90 when the rod engages the limiting means, and cutting discs from the rod while maintaining the said angular relationship.

6. The method of producing electrical contact discs from an elongated rod of contact material including the steps of rotating the rod, bringing the rotating rod and a cutting wheel into cutting relationship, cutting discs having conical surfaces from the rod by relatively moving the rod and the cutting wheel into cutting engagement while maintaining an angle between the rod and the cutting wheel of less than 90, and subsequently rounding 01f the apex and sharp edges of the conical surfaces so formed to provide discs having a generally spherical contact surface.

References Cited by the Examiner UNITED STATES PATENTS Honiss 82-47 Matheus 8283 Hamilton 82-87 Merritt 8247 Clemens 8246 Sarulla 8247 Lipkins 144323 WHITMORE A. WILTZ, Primary Examiner.

WILLIAM W. DYER, 111., Examiner. 

1. THE METHOD OF PRODUCING ELECTRICAL CONTACT DISCS FROM AN ELONGATED ROD OF CONTACT MATERIAL COMPRISING ROTATING THE ROD, BRINGING THE ROTATING ROD AND A PLANAR WHEEL CUTTING DEVICE INTO CUTTING RELATIONSHIP WITH THE ROD AND RELATIVELY MOVING THE CUTTING DEVICE AND THE ROD IN A PLANE AT AN ACUTE ANGLE TO THE AXIS OF THE ROD TO SEVER THE ROD BY PROGRESSIVELY CUTTING THE ROD ALONG SUBSTANTIALLY ONE-HALF A CHORDAL LENGTH AT THE DEPTH OF CUT. 